Migraine preventives are drugs taken daily to cut down how often and how badly attacks occur, and the recognised classes are beta blockers, calcium antagonists, antiepileptics, and antidepressants. Among the choices, Propranolol represents the beta blocker class and is a textbook first-line preventive. Flunarizine is a calcium channel blocker that is a well established preventive option for recurrent migraine. Topiramate is an antiepileptic that carries a formal indication for migraine prevention and is considered first-line. The odd one out is Levetiracetam: although it is an antiepileptic like topiramate, it has no recognised role in migraine prophylaxis and is reserved for epilepsy management. By elimination, the only agent that does not belong to the migraine prophylaxis list is Levetiracetam.\[\boxed{\text{Levetiracetam}}\]